1. Field of the Invention
The invention relates to a control apparatus for a power transmission system including a plurality of power transmission paths provided in parallel with each other between a driving force source and a drive wheel.
2. Description of Related Art
There is well known a power transmission system including a plurality of power transmission paths. The plurality of power transmission paths are provided in parallel with each other between an input rotating member and an output rotating member. Power of a driving force source is transmitted to the input rotating member. The output rotating member outputs the power to a drive wheel. This is, for example, a power transmission system for a vehicle, described in International Application Publication No. 2013/176208. International Application Publication No. 2013/176208 describes the power transmission system for a vehicle, including a power transmission path through a continuously variable transmission and a power transmission path through a gear train. The power transmission paths are provided in parallel with each other between an input shaft and an output shaft. In this power transmission system for a vehicle, when an intermesh clutch and a first clutch mechanism provided on the input shaft side with respect to the intermesh clutch are engaged, the power transmission path through the gear train is established. When a second clutch mechanism is engaged, the power transmission path through the continuously variable transmission is established. A speed ratio that is established by the power transmission path through the gear train is set to a value larger (that is, lower) than the lowest vehicle speed-side speed ratio (that is, maximum speed ratio) that is established by the power transmission path through the continuously variable transmission. Therefore, for example, when the vehicle starts moving, the power transmission path through the gear train is established (selected) by engaging the first clutch mechanism and the intermesh clutch, with the result that a large driving force is allowed to be generated in the vehicle.
Incidentally, in the power transmission system for a vehicle, described in International Application Publication No. 2013/176208, during a stop of the vehicle, it is desirable to establish the power transmission path through the gear train in advance in preparation for a start of the vehicle. For example, when an N-to-D shift for changing a shift position of a shift operating member from a neutral position to a forward drive position is performed during a stop of the vehicle while the driving force source is being operated, the power transmission path through the gear train is established. At this time, because of the structure of the intermesh clutch, when there is relative rotation between input and output elements, the intermesh clutch may not be engaged because of the fact that input-side and output-side teeth provided in the intermesh clutch reject each other. In this way, there is a case where the intermesh clutch may not be engaged in a state where the first clutch mechanism is engaged. For this reason, it is required to establish the power transmission path through the gear train by engaging the first clutch mechanism in a state where the intermesh clutch is engaged. Therefore, when the intermesh clutch is not engaged, the intermesh clutch is engaged in advance of engagement of the first clutch mechanism. However, depending on the phases of counterpart members (for example, spline teeth) that mesh at the time of engagement of the intermesh clutch in a state where rotation of the input and output elements of the intermesh clutch is stopped, there is a possibility that an engagement fault (uplock) of the intermesh clutch occurs. The engagement fault (uplock) is such a fault that an engagement operation of the intermesh clutch does not proceed and, as a result, the intermesh clutch is not engaged. If such an uplock occurs, the power transmission path through the gear train is not established, so it is disadvantageous in the startability of the vehicle. The above-described inconvenience is not publicly known.